Speed of light waves & photons

About the speed of light waves & photons
Speed of light waves
  • The speed of a light wave is a measurement of how far it travels in a certain time.
  • The speed of light is usually measured in metres per second (m/s).
  • Light travels through a vacuum at a bit less than 300,000 kilometres per second.
  • The exact speed at which light travels through a vacuum is 299,792,458 metres per second.
  • Light travels through other media at lower speeds.
  • A vacuum is a region of space that contains no matter.
  • Matter is anything that has mass and occupies space by having volume.
  • When discussing electromagnetic radiation the term medium (plural media) is used to refer to anything through which light propagates including empty space and any material that occupies space such as a solid, liquid or gas.
  • In other contexts, empty space is not considered to be a medium because it does not contain matter.
  • When light is described in terms of photons rather than waves the following points are important:
Speed of photons
  • Light exhibits wave-particle duality, meaning it can be described as both a wave and a particle (photon).
  • Photons are massless particles that travel at the speed of light.
  • Photons carry energy and momentum in quantized discrete units.
  • “Quantized discrete units” refers to the way energy and momentum are carried by photons.
  • In quantum mechanics, certain physical properties, such as energy and momentum, are quantized, meaning they can only take specific discrete values rather than a continuous range of values.
  • For photons, this means that their energy and momentum come in distinct, non-continuous packets or “units.”